This invention relates to porous structures and more particularly, to microporous structures made from synthetic resin.
Microporous structures, usually in the form of membranes, have a high degree of utility in filtration which is a very important industrial process. For example, filtration is used in the clarification and cleaning of fluids, in gasification and degasification, in biological waste treatment, in waste water treatment, in oil and water separation processes, in oil reclamation processes, and in air analysis including purification, dust collection, aerosol filtration, and oil entrapment. Since the microporous structures used for filtration are usually in the form of thin membranes, they have very little structural strength, which limits how the membranes can be used. For example, because of their lack of strength, membrane filters cannot be easily back flushed. Also, membrane filters are primarily surface filters in which the filtered residue is separated from the filtrate at the surface of the filter, as opposed to depth filtration wherein the filtered residue is accumulated in the body of the filter.
Filtration with membranes is a useful process, when solid particles are being filtered out from a fluid and it is desired to accumulate the filtered residue as a filter cake on the surface of the filter. However, when such a filter cake is formed, it would be advantageous to separate the filter cake from the membrane by back flushing the filter, but because of the lack of mechanical strength of the membrane, separation by back flushing is difficult to accomplish.